Growing food is a major concern on space missions. There is a limitation on the amount of food that could be taken into space and this is why growing some good is a necessary requirement.
And new studies have shown that you could grow food and urine if you are in Mars. The experiments are currently going on to make us of synthetic and human urine to make food items and apart from this, the water on International Space Station, including the waste water, will be recycled for the purpose of growing food.
The experiment is still in its inception and the scenario would be clearer as we go forward.